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Eleven cell lines have been establisbed from chronic lymphocytic leukemia (CLL) cells by transfection with human c-myc and human N-ras and mutant p53's (ph53-ser151, ph53-ile247, ph53-trp248 and ph53-leu$\sp{273}).$ These were obtained from three cases out of a total of 137 samples from 51 cases of CLL so transfected. Surface marker profiles confirm that all transfectants have arisen from the original CLL cells. They retain the CD5 antigen characteristic of B type CLL. Immunoglobulin gene rearrangement studies are also generally the same as the original cells although two of the cell lines show presumably secondary changes. They do not form colonies in semi-solid media. Two were tested and were negative for tumorigenicity in nude mice. Susceptibility to transformation was not related to clinical status. Of the 3 cases that transformed, one was Rai stage 0, another Rai stage 1 and another Rai stage 4. The Rai stage 0 case had never been treated. Although the original cells were Epstein Barr nuclear antigen (EBNA) negative, EB virus was detected in the original cells and the cell lines using the polymerase chain reaction (PCR). The cell lines are EBNA positive but negative for EBV LMP. It is noted that the cell lines from two of the cases have trisomy 12 which is the commonest karyotypic abnormality found in CLL. While the majority of CLL cells appear resistant to transformation in vitro with myc and ras, it does occur in a small percentage (about 8%). EBV is present in latent form (LMP is negative) but may play an ancillary role in transformation. The cell lines established may be of value in in vitro testing of drugs of possible therapeutic value in CLL and in studying molecular changes associated with CLL. Comparison with transfection of follicular lymphoma cells was also carried out. Cells from 9 cases of Follicular lymphoma (FL) were transfected with human c-myc and N-ras and mutant p53's (ph53-ser151, ph53-ile247, ph53-298 and ph53-leu273. Five cell lines have been established by transfection with mutant p53's. No cell lines was obtained from transfection with myc and/or ras. The cell lines had the same light chain monoclonality as the original FL cells. Immunoglobulin gene rearrangement studies showed that the original cells and cell lines from case BM were identical. However, surface marker studies showed that the original cells and cell lines from case BM and cell line from case FW lacked the CD10 antigen which is common in FL. Both cases also lack evidence of bcl-2 rearrangement (t(14;18)), which occur in 85% of FL, with the mbr probe either by Southern blot or PCR and with the karyotype of the cell lines. (Abstract shortened by UMI.)